1. Field of the Invention
The invention relates to a communication system comprising a communications network coupled at least to a terminal unit.
2. Discussion of the Related Art
From WO 92/11724 or the number about this subject of the journal net--Zeitschrift fur angewandte Telekommunikation", Net Special Mar. 12, 1993, pp. 8 to 18, is known a communication system which comprises a communications network (switched telephone network, service control point) with a plurality of switching points and terminal units coupled thereto. Certain switching points included in the communications network are used, on the one hand, to switch functions to several terminal units (for example, telephone traffic) or further switching points and, on the other hand, to switch over to a further network (overlay network) which provides special services. A service of the German Postal Service Telekom is, for example, the private information service Tele-Info-Service.
If a subscriber dials a special service number (for example, 0190 . . . ), this number designates a switching point (service switching point) which establishes an appropriate connection to the further network provided for services. Specific switching points not only switch through telephone connections, as they normally do, but also process calls and switch them through to the service-processing network. To this end such a switching point is more extensive, compared with a switching point provided only for telephone traffic, and thus the communication network is modified.